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Doubt on mixer biasing

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ram@419

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Hi i have a small doubt regarding mixers........

While testing a mixer we wont give ny biasing for a mixer..
We simply give rf and lo signals and check for the if...
I think mixer internally consists of some diodes....how can these diodes get activated (biased)...with out having supply..

Plz clarify my doubt....
Thanks and regards
ram
 

In a few words:
In a passive mixer, the signal applied to the LO port manages the conduction of the diodes.
For this reason the LO signal must not be below a certain level.
Regards

Z
 
As Zorro wrote, a mixer needs its diodes to be "pumped" by a LO input power. LO power drives AC and DC current through the diodes, alternatively opening and closing them. When you inject a low-level RF signal into it, the diode non-linearity around the I/V "knee" will generate harmonic combinations of the LO and RF frequency. Some of then are passed to IF output and filtered.
Instead of LO pumping power, setting the diode bias to get their operation point close to the I/V "knee" can be done by a DC bias. Then LO power can be ~10 times lower, and the mixer still operates well.
Find a good book on mixers, and better- make one and play with it! You will learn the art.
 
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